Nimona is about a supervillain, Lord Ballister Blackheart, who teams up with a young girl, Nimona, who also is a very powerful shapeshifter. The comic takes place in a kingdom where the good-guys aren't as good sometimes. The setting appears to be like a fantasy world, but there are elements of modern technology, magic and super science.
The comic is gaining momentum. HarperCollins has purchased the rights to Nimona to produce two graphic novels in 2015. Slate Magazine awarded the comic the Cartoonist Studio Prize for Best Web Comic of 2012. Io9 favorably compared Nimona to the Venture Bros (though, with fewer pop-culture references and not quite as vulgar, in my opinion).
Stevenson's art style is very unique and stylized. She leans way towards an artistic style rather than realistic art, which really adds to the feel and spirit of the comic. It's clear that the web comic will translate very well to print.
Stevenson updates Nimona on Tuesdays and Thursdays.